DESCRIPTION: This project is designed to elucidate mechanisms that control the specialization of body segments in Drosophila. There are three main areas of investigation. First, Dr. Duncan will study a region within the Bithorax Complex (BX-C) that is involved in controlling the expression of at least one of of the three homeotic genes in this complex. Second, Dr. Duncan will attempt to identify and characterize proteins that interact with the product of the pair-rule gene fushi tarazu (ftz), and third, Dr. Duncan will analyze the structure and function of the homeotic gene spineless-aristapedia (ss). Investigations in these three areas have been ongoing in Dr. Duncan's laboratory during the last funding period. The first part of the project will focus on a peculiar transvection-type interaction between the iab-5,6,7 cis regulatory regions of the Bithorax Complex and the promoter of the Abdominal- B (Abd-B) gene. Preliminary studies have indicated that this interaction is mediated by a < 9 kb DNA segment between iab-7 and Abd-B. Dr. Duncan has termed this segment the transvection mediating region (tmr). By combining overlapping deletions in which Abd-B is deleted from one chromosome and iab-5,6,7 is deleted from the other, Dr. Duncan has shown that the iab-5,6,7 region is able to regulate Abd-B in trans. This transvection is unusual because it is independent of homology in the target gene and is difficult to disrupt by rearrangement heterozygosity. Dr. Duncan's genetic studies indicate that the tmr must be present in cis with iab-5,6,7 in order to trans regulate the Abd-B gene. He suggests that the mechanisms used for this trans regulation are the same as those used for the cis regulation of Abd-B. In the next funding period, Dr. Duncan proposes to map the tmr with greater precision, determine if the tmr is required for cis as well as trans regulation of Abd-B, and see if it has the properties of "pairing sensitive" sites found in several other Drosophila genes. Futhermore, he plans to test if the tmr mediates direct physical contact with Abd-B or functions by promoting transcription of the iab regions. He also proposes to conduct mutant screens to identify genes required for the trans regulation of Abd-B by iab-5,6,7. The second part of the project will focus on the functional analysis of the ftz homeodomain protein. Previous work has shown that the segmentation functions of ftz can be executed by the N-terminal 157 amino acids of the 413 in the ftz protein. The function of ftz in the nervous system, in contrast, is independent of this N-terminal region and requires the C-terminal portion of the protein, including the homeodomain. Dr. Duncan hypothesizes that because the N-terminal region of ftz does not contain any known DNA-binding motifs and does not appear to bind DNA, that it functions by interacting with other proteins. Accordingly, he proposes to use genetic and molecular appraoches to identify and characterize these proteins. The third part of the project will focus on the ss gene. The peculiar phenotype of some ss mutants motivates this part of the project: distal segments of the legs develop in place of distal segments of the antennae, suggesting that ss may play a role in defining the proximodistal axis of the appendages. The ss gene encodes a basic helix-loop-helix protein with two DNA binding domains and curiously, is also homologous to the vertebrate aryl hydrocarbon receptor, also known as the dioxin receptor. The structure of the protein suggests that it forms heterodimers, possibly different ones in specific tissues to execute different developmental programs. Accordingly, Dr. Duncan proposes to use genetic and biochemical approaches to identify proteins that might dimerize with the ss protein. He also proposes to map functional domains in this protein, much as he has already done for the ftz protein.